Field of the Invention
The present disclosure relates to the field of shoe soles and in particular to shoe soles constructed for energy restoring and the controlled transfer of energy.
Description of the Related Art
Numerous shoe constructions have been proposed for many shoe types and a variety of styles. Major considerations in the design of any shoe include protection and comfort of the foot. For shoes that are primarily used for extensive walking, jogging or running other considerations may come into play. In particular, the pounding of a foot on a hard surface results in the imparting of repeated shocks to the skeletal and muscular systems of that person. The use of springs to absorb these shocks in the soles of shoes is well known, but traditional coiled and leaf spring applications have distinct limitations.
The design of foot orthotic or prosthetic load transition structures within existing patents has been generally limited to the employment of springs and dampers to absorb shock, store energy and then released the stored energy. Yet existing references do not fully appreciate nor address the complexity of bone-muscle-tendon-ligament interactivity during the gait cycle, which is a direct result from a load deterioration curve. This deterioration curve is determined by the reactive stress and strain forces on biological structures of the lower extremities, which exhibit both nonlinear and viscoelastic behavior.
Nonlinear behavior in biological structures as they pertain to gait can be characterized, in part, by deformation and strain as a result of load and stress. During tensile tests, this is evident by the longitudinal aligning and crimping of collagen fibers. This is referred to as the toe region followed by a linear phase of load elongation behavior.
In addition to nonlinear behavior, biological structures such as tendons are viscoeleastic, in that true tensile properties are rate dependent. When viscoelastic materials experience a load, the exhibited hysteresis is characterized by a shift in load deformation response until equilibrium is reached. The behavior of ligaments can be attributed to tensile axial loads, which elastically deform the tissue. With age, ligaments and tendons withstand less loading, leading to over-stretching and failure.
Forces and movements affect the way in which all body segments move. A force is a quantity that changes the velocity and/or direction of an object. The magnitude of this force is equal to the mass of an object multiplied by the acceleration of the object, (kg*m)/s2, or Newton (N). A moment is the quantity that changes the angular velocity of an object. The magnitude of moment is equal to object's moment of inertia (objects mass and distribution of mass) and its angular acceleration, the unit is the newton-meter (N-m). The concept of static equilibrium is when no accelerations are occurring in the musculoskeletal system. If there is no acceleration, the moment forces must be zero.
Human gait, however, is a dynamic event and these moments and forces are high across the musculoskeletal system. The prior art provides shock absorption and energy transfer to and from the heel, but is not constructed with the ability to affect the acting moments and forces about the foot, lower extremities, back, and their related musculoskeletal structures. In this regard, the prior art references address different forms of the shoe sole including separate midfoot arch support, but these shoe soles lack an integrated approach for the transfer of loads during the gait cycle.
Because muscles originate and terminate close to joint centers, they generate large loads of force to resist the moments about each joint. This load generation, in turn, causes compression about the joint surfaces, resulting in large joint reactive forces. This is especially true with regards to the lower extremities, where the quantities of these forces can equal multiple times and individual's body weight.
A device is needed that provides enhanced stability to the lower extremities throughout normal joint movement. This device can enhance the stability of joints and limit peripheral or edge loading such that it will only occur with large changes in direction of load and changes in joint contact positions. Similarly, the axial load demands that ligaments experience that are dissipated through energetics can be reduced.
Too often spring devices in shoe sole application serve as a load transfer and storage device to and from the heel, but fail to further the natural progressive transfer of load and deformation of foot bones under the load for a normal gait. This deformation is needed to support the midfoot during normal gait. The compression and tensile forces affect the midfoot simultaneously, increasing pressure on the peripheries of the foot, specifically the dorsal surface of foot.
A device is needed that provides structural support to the dorsal surface of the foot while accommodating kinematic deformation of the foot. The device enhances joint kinematics in a way that balances the reactive forces in the lower extremities as a result of gravity, inertia, muscle contraction, and related biological structures. This balance of forces is needed to reduce energy levels on the joints, preventing various gait and medical problems and heretofore has remained unaddressed by the prior art.